In a majority of the prior art insulated electrical transmission lines, commonly referred to as transmission cables, the dielectric covering or primary electrical insulation consists wholly or partially of organic materials that are susceptible to breakdown when subjected to prolonged temperature incursions of over 100.degree.C. For example, the widely accepted oil impregnated paper wrapped conductor cables are operated so that the temperature at the conductor-insulation interface does not intentionally exceed 85.degree.C for any sustained period of time. This greatly restricts the power-handling capability of such cables. In spite of its limitations oil-paper cable dominates the transmission cable market. An example of a prior art transmission line having such a cable is found in U.S. Pat. No. 3,429,979 of E. L. Davey issued Feb. 25, 1969.
It is quite apparent to those skilled in the art that transmission cable technology would be advanced if a cable could be found which provided an improved outward transfer of heat away from the conductor. The advancement would be greater if at the same time the dielectric material surrounding the conductor could withstand prolonged temperature incursions of 200.degree.C or more without catastrophic failure. Accordingly, the electric power industry has expended and is continuing to expend, at an increasing rate, large sums of money on research and development work in search of an improved transmission cable. Although workable cable systems have resulted from these efforts the new systems have not been able to gain dominance over oil-paper cable systems.
Glass materials in general have long been recognized for their dielectric properties and have been used widely for dielectric members in electrical equipment. It is also well known that most glass materials have relatively high coefficients of heat transfer and are not subject to chemical decomposition upon being heated. The softening point temperatures of most glass materials fall between the melting point temperatures of aluminum and copper, the commonly used conductor materials. Yet, in spite of all of these attributes, no one has disclosed, prior to the date of this invention, a high voltage electric power transmission cable which utilizes a glass casing as the primary electrical insulation and wherein the casing comprises a plurality of longitudinally seamless tube sections bonded together end to end.